In many mouse models of neural tube defects, such defects occur in less than 100% of individuals, reflecting a phenomenon that geneticists call incomplete or partial penetrance. It is known that phenotype penetrance can be modulated by genetic background. However, this does not explain how, within a single inbred strain of genetically identical individuals, some have a defect while others do not. Since all mutant animals carry the same genetic alteration, the mutant allele itself cannot explain the phenomenon of partial penetrance. Therefore, other risk factors must exist in NTD-affected progeny. We hypothesize that -in the absence of genetic variation- NTD risk is associated with variable expression of genes and pathways that are critical for normal neural tube closure. Specifically, we propose that differences between individuals have great explanatory power for partial penetrance, when only some individuals manifest an NTD. Then, to identify specific factors that convey NTD risk to those individuals, it is necessary to explicitly focus on variabiliy. This idea is in contrast to conventional approaches that minimize variation, and thus provides a highly innovative conceptual framework. In our experimental paradigm it is possible, for the first time, to unequivocally identify NTD-prone individuals before the process of neural tube closure is completed. This provides us with the unique opportunity to develop and test predictive models for an individual's NTD risk. Our overarching goals are 1) to discover new risk factors from gene expression patterns in NTD-susceptible individuals, 2) to define expression signatures that can predict individual NTD susceptibility, and 3) to study the in vivo function of such risk signatures in defective neural tube closure by CRISPR/Cas transgenic technology. Determining to which extent risk signatures are shared among or unique to individuals has enormous biological significance, as these alternatives prompt fundamentally different strategies for prevention of NTDs: common risk factors would implicate specific biological pathways, whereas with individually distinct risk signatures, one would have to target the epigenetic mechanisms that cause variability. The need for more effective prevention is highlighted by the findings that folic acid supplements and food fortification together can prevent only 30% of the neural tube defects in the US, resulting in 3000 pregnancies affected by a defective neural tube closure every year in the US alone. A better understanding of the molecular mechanisms that confer susceptibility is required for development of new targeted strategies to prevent neural tube defects.